Need help with power supply for Pacific RIAA

[Dmeister]

Hello everyone. I just registered here since I'm getting into DIY audio. I just built the Pacific RIAA. Here's the schematic:

An externally hosted image should be here but it was not working when we last tested it.

The thing is. I have no idea on what power supply to use. I'm not planning on anything expensive and my first idea was to buy something like a laptop charger or something similar. What i need to know is: How many volts and how much current do i need for a power supply for a project like this. Thanks ahead !

 

[bob91343]

It says 24 Volts but you can get by with a lot less. Almost no current draw so you can use a wall wart. Just make sure you put an electrolytic capacitor from +24 to ground.

 

[Dmeister]

Thanks a lot, man Would it work without the electrolytic cap ?

 

[leadbelly]

Thanks a lot, man Would it work without the electrolytic cap ?

Where is there an electrolytic? They are all non-polarized.

 

[Dmeister]

Where is there an electrolytic? They are all non-polarized.

There's no electrolytics in this schematic, although there is this schematic which is a slight variation and it includes a 2200uF electrolytic placed between ground and the +24V.

An externally hosted image should be here but it was not working when we last tested it.

 

[leadbelly]

There's no electrolytics in this schematic, although there is this schematic which is a slight variation and it includes a 2200uF electrolytic placed between ground and the +24V.

That cap is just the power supply filter cap. You don't need it specifically, BUT this circuit has poor PSRR, so you will need a good clean PS. Personally, I would use a 3 terminal regulator such as LM317 or LM7824.

 

[Dmeister]

I'm really, really new to all this. So basically if i put in the 2200uF cap, the sound will be somewhat better, right ? Will it make a big difference in sound quality ?

 

[leadbelly]

Will it make a big difference in sound quality ?

That is a complex question to answer, and I think you will just get confused.

At the risk of oversimplifying, yes I can see where Bob would recommend that if you are going to use a laptop charger, then use a big filter cap to get as much ripple out of the supply as possible.

 

[Dmeister]

But it would still work relatively good without it ? I'm no audiophile so i probably don't have ears accurate as say, yours. So I probably won't notice too much of a difference.

 

[leadbelly]

But it would still work relatively good without it ? I'm no audiophile so i probably don't have ears accurate as say, yours. So I probably won't notice too much of a difference.

For that circuit, if you don't have a good low ripple supply, you will hear lots of hum, and you won't need golden ears to hear it! That being said, sure, leave the big cap out and report back when you try it out.

 

[Dmeister]

I've just found an old Polish 4700uF electrolytic cap. I think it's working. Will it do the job ? Also I've found an old Polish transformator which i'm not really sure how much voltage it gives (it's from an old radio if it helps). Should i test it somehow ? Would it be dangerous to test it ? The radio can also use batteries so I'm guessing the out voltage of the transformator is about 12V or something similar.

 

[Dmeister]

Apparently, the transformator was malfunctioning and i blew a fuse. So i'll get another one. Can anyone tell me whether the 4700uF Cap would work instead of the 2000uF one ?